In a conventional RFID (radio frequency identification) transponder chip, a coil having a plurality of windings is usually used as an antenna for communicating with an RFID reader. The antenna is directly arranged on the RFID transponder chip (on-chip coil) or on a body coupled to the RFID transponder chip. The on-chip coils usually have a plurality of layers which are connected by means of lines (vias). As a result, at least geometrical boundary conditions to be complied with can be predefined for the logic of the chip, thus resulting in design and/or technical restrictions. On account of the use of inductive coils for communication, communication is dependent on resonances. Coupling and therefore communication are often possible only in the high-frequency range (HF) or in the ultra-high-frequency range (UHF).
In the case of an inductive, frequently inhomogeneous, magnetic field for communication, as in an RFID transponder chip with a coil as an antenna, clear separation of a coupling area, in which the antenna is formed, from an electronic area, in which the logical components of the transponder chip are arranged, is possible only with difficulty, which may influence communication. In addition, an on-chip coil causes self-heating of the corresponding transponder chip. Not only eddy currents, caused by the magnetic field, but also the high induced currents in the coil may result in the transponder chip being heated to a relatively severe extent. In addition, RFID technology is poorly suited to identifying objects, for example capsules, jewelry or coins, which have a lot of metal or are formed largely from metal since the metal has an adverse effect on RFID performance.
In order to be able to couple sufficient energy into RFID transponders having very small antennas, for example integrated antennas on or in the transponder chip, a very concentrated field is often applied to the RFID transponder. Therefore, the RFID transponder chip and the antenna of the RFID reader are often positioned exactly with respect to one another. This is only possible if the exact position of the RFID transponder chip is known and the antenna can actually be positioned exactly with respect to the position of the RFID transponder. Large antennas in the form of large loops, as are conventional in other RFID systems, often cannot be used since they do not enable a sufficient field concentration. Although antennas having small loops can enable the required field concentration, they have the great disadvantage that the position of the RFID transponder chip must be known exactly in order to then bring the small loops of the antennas very close to this position. However, often either the position is not known and/or exact positioning of the antenna of the reader is not possible or acceptable.